1. Field of the Invention
This invention relates to a printing press of the type having a removable printing sleeve on a printing roll. Such presses are typically used for flexographic printing.
2. Description of the Prior Art
Demountable printing sleeves are now common in the art of flexographic printing, and a variety of techniques for fitting and demounting such sleeves on printing rolls are known. A typical modern printing sleeve is disclosed in Julian, U.S. Pat. No. 4,144,812.
While the art of moving a printing sleeve on and off a printing roll is well developed, the need to manipulate the printing roll itself during the exchange continues to present a serious bottleneck in the operation of flexographic printing presses. In most printing presses the entire printing roll has to be removed from the printing machine, and then replaced after the printing sleeve is changed. This is tedious, labor intensive, and results in a high level of unproductive time for the printing press.
In Hollis, U.S. Pat. No. 4,119,032, it is shown that a printing sleeve can be removed from a printing roll while the roll remains substantially in its working position. In the Hollis apparatus, the printing roll rides in a bearing block assembly, the entire assembly being axially removable from the mandrel of the roll. During the interval when the roll is deprived of the bearing block's support, it is maintained in position by a counterpoise that bears downward on the opposite end of the roll mandrel. Once the bearing block is removed, the printing sleeve can be slid off the roll and replaced.
Removal of bearings from the shaft of a printing rolls is difficult, particularly if the bearing is press-fitted onto the shaft. The use of set screws to prevent the bearing block from axially sliding on the shaft is likely to score the shaft, which can make subsequent removal of the bearing even more difficult. The scoring can shorten the useful life of the printing roll, and necessitate expensive re-milling in order to restore it to operating condition. Alternatively the bearing could be freely slidable on the shaft. The latter approach is used in the above noted Hollis patent; however it requires complex adjustable axial restraints to maintain the bearing in proper alignment during operation.